Occupational contact dermatitis is often of multifactorial origin, and it is difficult to determine the relative significance of the various contributing factors. Contact allergies are relevant in 20-50 of recognised occupational contact dermatitis cases. The reported frequency in different studies varies, depending on differences in how occupational diseases are notified and recognised, in types of occupation in a geographical area, and the "quality" of the dermatological examination, including the accuracy of the diagnostic patch-test investigation. However, the clinical relevance of the reported contact allergies is often uncertain. Many occupational contact dermatitis patients with documented contact allergies develop chronic eczema, in spite of work changes and attempted allergen avoidance. Recognition/non-recognition of a notified case may be based on circumstantial evidence, because of difficulties in the establishing of a firm proof of work exposure and subsequent development of skin disease. Reliable quantitative exposure measuring techniques are needed. Methods are developed for the measurement of exposure to allergens such as nickel and acrylates, which makes it possible for exposure-effect relationships to be established with increased certainty. For prevention of allergic contact dermatitis it was a major step forward, with mandatory ingredient labelling of cosmetic products. However, improved labelling of the presence of contact allergens in household and industrial products is needed. For the identification of hazardous contact allergenic compounds, guinea pig or mice assays are still required. The local lymph node assay (LLNA), which is an objective and sensitive mouse assay has now been internationally validated and accepted.
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